Wafer container with overlapping wall structure

ABSTRACT

Improvements in a semiconductor wafer container including improvements in side protection to the wafers, improved cover design to minimize rotation, a simplified top cover orientation mechanism and an improved bottom holding mechanism for automation. The side protection to the wafers is with multiple staggered inner and outer walls. The improved cover design improves alignment of the top and bottom housings and minimizes rotation of the housings in transit or motion. The housings have a recessed tab ramp feature with bi-directional locking that also increases the rigidity of the containment device when the two housings are assembled. The improved bottom holding mechanism for automation is an integrated feature that is molded into the bottom housing and not assembled in a secondary operation. The molded integration reduces tolerance errors that are present in assembling multiple pieces and joining multiple pieces.

CROSS REFERENCE TO RELATED APPLICATION

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

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THE NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

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INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC

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BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to improvements in a container for thetransportation of semiconductor wafers. More particularly, the presentwafer container includes improvements in side protection to the wafers,improved cover design to minimize rotation, a simplified top coverorientation mechanism and an improved bottom holding mechanism forautomation.

2. Description of Related Art Including Information Disclosed Under 37CFR 1.97 and 1.98

In the processing of semiconductor wafers the typically must betransported either between processes or to other facilities. Thesemiconductor wafers are fragile and damage to the surface of the waferscan make the wafer useless for the intended purpose. Because of the highpotential for damage to the wafer the semiconductors must be packagedand transported to minimize harm. In transportation, multiplesemiconductor wafers are stacked into a transportation container. Therehave been a number of containment products and patents have been soldand patented to try and minimize damage to these silicon wafers.Exemplary examples of patents covering these products are disclosedherein.

U.S. Pat. No. 6,193,068 issued Feb. 27, 2001 to Lee Lewis et al., andU.S. Pat. No. 6,341,695 issued Jan. 29, 2002 to Lee Lewis et al.,disclose a containment device for retaining semiconductor wafers. Thispatent discloses two concentric walls on the top and bottom housingsthat nest to protect the semiconductor wafers. Double walls weredesigned to protect the wafers from the direct transmission of forcesthat may contact the outer wall. While the nesting walls provideprotection from side impacts they do not provide flexibility to absorband cushion a side impact or drop. The combination of an outer wall anda gap provide the protection. Damage may also occur if the force is suchthat the outer wall flexes enough to interfere with the inner wall,thereby damaging the wafers. That can cause the semiconductor wafers toshift and scratch.

U.S. Patent Publication Number US2009/0095650 that was published on Apr.16, 2009 to James D. Pylant et al., discloses a wafer container withstaggered wall structure. In this published application the design islimited by the amount overlap of the inner and outer walls by the designof its staggered walls. The walls were limited to 5% overlap, with 95percent of the outer wall not located in adjoining angular sectors. Thisand other top cover rotation locating mechanisms use either an innersurface of a feature on the top cover or an exterior surface of afeature on the top cover to secure the top cover in place and preventrotation.

U.S. Pat. No. 6,550,619 issued Apr. 22, 2003 to Gregory W. Bores et al.,discloses a shock resistant variable load tolerant wafer shipper. Thispatent uses four inner tapers walls with a variable amount of cushionsplaced between the semiconductor wafers to pack and cushion thesemiconductor wafer. While this patent allows for a variable amount ofsemiconductor wafers to be packed within the shipper the cushioningrelies on the variable amount of cushions placed between thesemiconductor wafers to reduce damage.

U.S. Pat. No. 7,040,487 issued on May 9, 2006 to Michael Zabka et al.,discloses a protective shipper with a corrugates inner containment lip.The corrugated inner lip provides multiple surfaces for the edges if thesemiconductor wafers to make contact with, but because the edges arecorrugated the tangential walls of the corrugation limit the flexing ofthe inner lips.

Some semiconductor wafer containers use a rotation locking design wherethe locating mechanism with an exclusive inner surface or exteriorsurface do not securely capture the wall that they are adjacent to inboth directions of rotation. These features only stop rotation in onlyone direction. The features must rely on a sister feature to stoprotation in the opposite direction which is generally located fartheraway and allows for more manufacturing tolerance to build up since it islocated at a greater distance. These deficiencies result in larger gapsbetween the plus and minus rotational limiting surfaces, thereby leadingto more rotational movement.

There are a number of prior designs that use top cover orientationfeatures with differing wall engagement angles or large latches asopposed to small slots. The new feature in this proposed wafer containerallows improved orientation that is not found in the prior art.

There are a number of different holding and clamping features in wafershipping containers. All of these prior designs rely on multiple partsto create a clamping lip. These designs have several drawbacks includingbut not limited to the parts not being rigid with respect to the bottomassembly because they must be sonic welded, bonded or snapped togetherand that secondary parts or assembly operations are more expensive toproduce.

The engagement of latches that secure the top and bottom housingstogether have a number of limitations. Specifically, prior art latchesprovide a raised straight slope ramp. The raise straight sloped surfaceis susceptible to damage and also, the straight slope does not providean ideal self gripping to engage between the top and bottom housings.The top cover orientation features use differing wall engagement anglesor large latches as opposed to small slots as presented in this pendingapplication.

What is needed is a semiconductor wafer container with improvements inside protection to the wafers, improved cover design to minimizerotation, a simplified top cover orientation mechanism and an improvedbottom holding mechanism for automation. This pending applicationsatisfies these requirements with novel improvements in the identifiedareas.

BRIEF SUMMARY OF THE INVENTION

It is an object of the semiconductor wafer container that has anoverlapping double wall. The wall structure comprises multiple outerwalls and multiple inner walls. The overlapping double containment wallincreases semiconductor wafer protection during impact or shipping. Eachinner wall shares a minimal percentage of a common angular sector witheach adjacent outer wall. The inner wall is generally very stiff anddoes not absorb and cushion the wafers if the container is dropped orsubject to impact. On the bottom assembly, the inner walls and outerwalls are positioned in an offset and overlapping configuration providesmaximum protection to the semiconductor wafers.

It is an object of the semiconductor wafer container to improvealignment of the top cover with the base. The alignment system includesreference tabs that are received by the cover and a visual identifierfor guiding an operator in the proper alignment of the two halves of thecontainer. The top cover orientation features prevent improperinstallation of the top cover to the bottom member. The top coverorientation feature is incorporated into the top cover that mates withthe features of the double locking location feature. This orientationfeature prevents installation of the top cover in plus or minus 90degree locations about the central axis.

It is an object of the semiconductor wafer container to provide animproved locking mechanism for securing two halves of a wafer containertogether. The bottom half comprises a wall structure perpendicular tothe base. The wall structure comprises segmented inner and outer walls,where each portion of the wall structure has a distinctive arc length.The arc length of each inner wall does not completely overlap with thearc length of any outer wall.

It is an object of the semiconductor wafer container to provide animproved engagement feature for the locking tabs. These improved tabsinclude a cover for a wafer container that engages to a base. The coverincludes one or more notches, each having a ramp that easily receivelatches from the base.

It is another object of the semiconductor wafer container to incorporatebi-directional rotation locking feature(s). These features improveorienting, the top member on the bottom member that decreases the amountof top cover rotation and movement with respect to the bottom member.This feature creates a double locking location that securely locates andlocks the top cover in place during top cover assembly. Thebi-directional rotation locking feature is located on both sides of theperpendicular top cover surfaces of a single wall on both the interiorand the exterior simultaneously. This improvement providesbi-directional locking of the captured surface decreases the amount oftop cover rotation and movement with respect to the bottom member andincreases the rigidity of the containment device when the members areassembled.

It is still another object of the semiconductor wafer container toinclude an improved holding and clamping feature to allow for automatedmachinery to latch onto and hold the bottom member and secure it firmlyto the machinery nesting locations. This mechanism is comprised of asingle piece feature that is molded into the bottom member. The holdingand clamping feature on the bottom member improves equipment interfacewhere these containers are used. The feature is a holding mechanism toallow for automated machinery to latch onto and hold the bottom memberand secure it firmly to the machinery nesting locations.

It is still another object of the semiconductor wafer container toinclude an improved curved latch recess for improved closure andretention of the containment device latches. In the improved latch andlatch recess the height of the latch is equal to or lower than the innerwall structure. This allows equipment to interface with the bottommember of the container without interference with the equipment andlatch height. A curvature on the mating surface provides superiorholding and self centering and gripping during handling and afterimpact. This recessed feature also protects the mating surface fromdamage when the top cover is disassembled from the bottom member. Thelatch recess and curved surface also provides increased latch retentionand container integrity during impact or shipping. This includes alowered latch equal to or less than the inner wall height.

Various objects, features, aspects, and advantages of the presentinvention will become more apparent from the following detaileddescription of preferred embodiments of the invention, along with theaccompanying drawings in which like numerals represent like components.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

FIG. 1 shows a perspective exploded view of the wafer container with aplurality of wafers disposed between the two wafer container halves.

FIG. 2 shows a top view of the bottom housing with the overlapping ribwall pattern.

FIG. 3 shows a detailed perspective view of the overlapping inner ribwalls.

FIG. 4 shows a top view of the bi-directional locking feature in thebottom housing.

FIG. 5 shows a perspective view of the bi-directional locking feature onthe bottom housing.

FIG. 6 shows a perspective view of the bi-directional locking feature onthe top housing.

FIG. 7 shows an inside plan view of the top housing showing theorientation features.

FIG. 8 shows inside plan view of the bottom housing showing theorientation features.

FIG. 9 shows a detail perspective view of the orientation key in the tophousing.

FIG. 10 shows a detail perspective view without the orientation key inthe top housing

FIG. 11 shows a detail perspective view of the clearance for theorientation key in the bottom housing.

FIG. 12 shows a detail perspective view of the interference for theorientation key in the bottom housing.

FIG. 13 shows a top perspective view of the bottom housing.

FIG. 14 shows a detailed perspective view of the hold down latch.

FIG. 15 shows a perspective cross section of the hold down latch.

FIG. 16 shows a perspective view of the top and bottom latch tabengaged.

FIG. 17 shows a side view of the bottom latch tab.

FIG. 18 shows a sectional view of the latch engaged between the top andbottom housings.

FIG. 19 shows a detailed view of the engaged between the top and bottomhousings.

FIG. 20 shows a perspective view of the top and bottom housings in anopen exploded view for reference of the internal components.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a perspective exploded view of the wafer container with aplurality of wafers disposed between the two wafer container clamshells. A plurality of semiconductor wafers 20, 21 and 22 are shownbetween the top 50 and bottom 100 housing with wafer separators 25. Theinside base surface 102 extends to the outside of the base surface 103where the bottom housing has a ribbed pattern 101 that supports thebottom of the bottom most semiconductor wafer 20 and provides increasedstructural strength to the fairly plainer base surface 102 and 103. Boththe top 50 and the bottom housings 100 have essentially planarrectangular or square bases. A plurality of inner rib walls 110 and 111of the bottom housing 100 protect the semiconductor wafers from shiftingside damage. These walls can flex to cushion side impact. They areformed in a segmented pattern in the bottom housing. The segmented ribsare shown and described in more detail with FIG. 2. A second set ofsegmented outer ribs 112 and 113 exist outside of the inner rib walls110 and 111. The rib walls exist in an overlapped 120 and 121 pattern toprevent debris from passing directly through the segmented ribs.

FIG. 2 shows a top view of the bottom housing with the overlapping ribwall pattern. Note that some features, such as bottom ribs, have beendeleted from the bottom surface 102 and 103 and the overlapping ribshave been moved slightly to improve clarity of the overlapping ribfeatures being discussed herein. FIG. 3 shows a detailed perspectiveview of the overlapping inner rib walls. While in FIGS. 2 and 3 only onesection of overlapping ribs is identified, the overlapping conditionexists in eight places in the bottom housing 100. While the preferredembodiment shows four inner rib walls 110-113 and four outer rib walls114-117 it is contemplated that a greater or lesser number ofoverlapping can be used. In FIGS. 2 and 3 the overlap 120 is labeled,and in the preferred embodiment the overlap angle is between 5 and 15degrees, but prototypes have been made using an overlap angle 120 of 7.5degrees. The ribs 110-117 are arc segments that extend perpendicularfrom the essentially planar base 102 and 103. These angles are variablebased upon the height of the rib, the material, the thickness of therib, the desired cushion and the distance between the inner and outerribs. In general the distance between the inner and outer ribs iscontrolled based upon the annular rib in the top clam shell housing.

The overlapping double wall provides maximum protection from shock orimpact to the exterior of the containment device by positioning theinner and outer wall in an offset and overlapping configuration as toincrease the protection of the semiconductor wafers from directtransmission forces by increasing the amount of flex movement allowed bythe outer wall. Increasing the flex tolerance of the outer wallincreases the overall shock absorbing ability of the containment device.This design also allows for a greater percentage of “wrap” around thesemiconductor wafer and therefore minimize lateral shift into the gapsbetween inner wall segments. Segmenting the inner wall makes it moreflexible and thus able to absorb and cushion the wafers if the containeris dropped or subject to impact.

As shown in FIGS. 1 and 3. The outer rib walls 114-117 need not be thesame height as the inner rib 110-113 walls. In some cases, the loweredexterior wall allows for greater top cover deflection during impactbefore it touches the inner wall. The image in the figures shows theexterior rib walls 114-117 at approximately ⅔rds the height of the innerrib walls 110-113 as shown in FIG. 1.

FIG. 4 shows a top view of the bi-directional locking feature in thebottom housing 100. FIG. 5 shows a perspective view of thebi-directional locking feature on the bottom housing 100. FIG. 6 shows aperspective view of the bi-directional locking feature on the tophousing 50. Starting with FIG. 6 the circular rib 51 is shown extendingfrom the planar base of the top housing 50. A “U” shaped rib extendsfrom the circular rib 51 to the outer edge 55 of the top housing 50 andaround to join back with the circular rib 51. This “U” shaped rib canexist in a variety of shapes to provide a key to ensure that it locksinto only one of four possible orientations with the bottom housing 100.This “U” shaped rib that extends to the outer edge 55 has an inside face53 and an outside face 52. Where the “U” shaped rib joins with the outeredge 55 there is an outside protection and support rib 54.

A pair of securing ribs consisting of an outer locking rib 131 and aninner locking rib 132 on the bottom housing 100 are configured to engageonto the opposing sides of the inside face 53 and an outside face 52 ofthe “U” shaped rib when the “U” shaped rib is engaged into the lockingcavity 130. Circular lock rib 133 is configured to fit within cavity 56on the top housing 50 along with the inner lock rib 132. When the ribdefined by items 52/53 is engaged into the locking cavity 130 thesefeatures improve orienting, the top housing 50 on the bottom housing 100that decreases the amount of top cover 50 rotation and movement withrespect to the bottom member 100. This feature creates a double lockinglocation that securely locates and locks the top cover 50 in placeduring top cover assembly. The bi-directional rotation locking furtherincreases the rigidity of the containment device when the members areassembled. The “U” shaped and is shown in an approximate orthogonalrelationship to three sides of the bottom housing 100. While only onelocation of the bi-directional lock is shown and described in detail,the feature exists on all four sides of the top and bottom housings.

FIG. 7 shows an inside plan view of the top housing showing theorientation features and FIG. 8 shows inside plan view of the bottomhousing showing the orientation features. FIG. 9 shows a detailperspective view of the orientation key in the top housing. FIG. 10shows a detail perspective view without the orientation key in the tophousing. FIG. 11 shows a detail perspective view of the clearance forthe orientation key in the bottom housing. FIG. 12 shows a detailperspective view of the interference for the orientation key in thebottom housing. For perspective, the area's 90, 91, 92 and 93 are shownenlarged and in perspective in FIGS. 9, 10, 11 and 12 to show theorientation tab 60 and how in allows or blocks seating of the top andbottom housings 50 and 100.

In FIG. 9 the orientation rib 60 is shown extending essentially normalfrom the circular rib 51 at a particular distance 62 from the corner ofthe “U” shaped rib 54 and 57. In FIG. 10 the orientation rib is notpresent in area 61 in the corner of the “U” shaped rib 54 and 58. Nowrefer to FIGS. 11 and 12 to see where the orientation rib 60 would beblocked or bypassed by the details. In FIG. 11 the dimension 106 betweenthe corner radius of curved lock rib 133 and the inner lock rib 132 isshorter than the distance 107 between the curved lock rib 134 and theinner lock rib 132 in FIG. 12. Upon placement of the top housing ontothe bottom in an out of proper orientation arrangement the longercircular block rib 134 would interfere with the orientation rib 60. Inthe correct orientation the shorter circular lock rib 133 would clearthe orientation tab 60.

From FIG. 7, a total of four orientation tabs are shown to allow thehousings to sit flat on the orientation tabs when the housings are notproperly aligned. The orientation tabs 60 prevent improper assembly ofsaid top housing and said bottom housing members from being installed 90degrees out of alignment.

FIG. 13 shows a top perspective view of the bottom housing. FIG. 14shows a detailed perspective view of the hold down latch. FIG. 15 showsa perspective cross section of the hold down latch. In views 13 and 15some parts of the circular ribs 110, 111, 114 and 115 are visible tohelp to provide a visual orientation for the pocket 80 and latchfeatures. The bottom housing 100 has an undercut hold down recessedpocket 80 with a latch surface tab 81 for a retention mechanism to holdthe housing in automated assembly. The latch surface is formed in amolding process with the molding of said bottom housing 100. The latchsurface 81 is located at a height that is equal to or lower than theplanar bottom surface 103 of said bottom housing 100. The latch surface81 further has an angled or curved entry surface 82. The pocket furtherhas at least two essentially vertical side walls 83 to self center saidbottom housing on said retention mechanism.

The height of the latch is equal to or lower than the inner wallstructure to allow equipment to interface with the bottom member of thecontainer without interference with the equipment and recess pocket 80and the latch surface 81. This recessed feature also protects the matingsurface from damage when the top cover is disassembled from the bottommember. In FIGS. 13 and 15 housing latches 70, 71 and 72 are shown.These latches secured the top and bottom housings together.

In FIGS. 13 and 15 a plurality of bearing ribs 85 are shown. These ribsare configured to distribute the load from a bottom housing stacked ontop of the top housing. Looking briefly at FIG. 18, it can be seen thatthe annular lip 87 of the bottom housing 100 is placed at a differentdimension from the annular lip 86 of the top housing 50. This allows thehousings to stack or nest. When stacking multiple wafer containerstogether the weight of the container when filled with wafers issignificant. Some wafer containers are enclosed in a protective plasticbag, and when the stacked bearing surface is small this creates a highbearing load which damages or punctures the protective bag. Calculationand testing has identified that multiple bearing surfaces 85 of greaterthan 2.25 mm² each with more than 4 bearing ribs 85 per quadrant willadequately protect the containers from damage and will also prevent theprotective plastic bags from being punctured or damaged.

FIG. 16 shows a perspective view of the top and bottom latch tabengaged. FIG. 17 shows a side view of the bottom latch tab. FIG. 18shows a sectional view of the latch engaged between the top and bottomhousings. FIG. 19 shows a detailed view of the engaged between the topand bottom housings. The bottom housing 100 has at least one latch thatengages in a corresponding notch 75 located on the top housing 50.

The top surface 74 of said latch 70 is located at a height 76 that isbelow the top surface of said at least one rib 141. The height 76 of thelatch 70 is equal to or lower than the inner wall 141 structure. Thisallows equipment to interface with the bottom member of the containerwithout interference with the equipment and latch height. This furtherreduces the possibility of damage to the latch 70 if the bottom housing100 is dragged on a surface. In the preferred embodiment there are fourlatches 70 and four corresponding notches 75 located in each cornerregion of said top housing 50 or said bottom 100 housing, but as few asone or two are contemplate as well as four or more latches. FIG. 19shows that the notch 70 has a curve entry ramp 77 and a recess 78 thatelevates the latch 70 above said entry ramp 77 and lowers said latch 70into the recess 78 to retain the latch 70 in the recess 78. When thelatch(s) are secured the top of the inner rib wall 111 is tightlyengaged and captured on the corresponding surface 84 of the top housing50. The notch 75 is located in a latch pocket 140 that protects thelatch 70 during handling and impact.

FIG. 20 shows a perspective view of the top and bottom housings in anopen exploded view for reference of the internal components. This viewprovides a view into the open cavity of the top housing 50 and thebottom housing 100 without obstruction of the semiconductor wafers.

Thus, specific embodiments of a semiconductor wafer container have beendisclosed. It should be apparent, however, to those skilled in the artthat many more modifications besides those described are possiblewithout departing from the inventive concepts herein. The inventivesubject matter, therefore, is not to be restricted except in the spiritof the appended claims.

1. A wafer container comprising: a top housing and a bottom housing thatnest together to form a clam shell housing with an inner cavity forstorage for at least one semiconductor wafer; said top housing having anessentially planar rectangular base with at least one rib that extendsperpendicular from said base in an essentially circular orientation;said bottom housing having an essentially planar rectangular base with aplurality of inner and outer arc sector ribs that extend perpendicularfrom said base wherein said inner and outer arc sectors ribs arearranged concentric with said at least one rib that extendsperpendicular from said base of said top housing, and said inner andouter arc sector ribs are formed such that the arc sector of at leastone inner rib overlaps the arc sector of at least two outer ribs whereinsaid overlap of said at least one inner arc sector rib and said at leasttwo outer arc sector ribs is an overlap of between 5 and 15 degrees whenmeasured from a concentric origin of said arc sector ribs.
 2. The wafercontainer according to claim 1 wherein said at least one inner rib andsaid at least one outer rib extend from said essentially planarrectangular base the same height.
 3. The wafer container according toclaim 1 wherein said at least one inner arc sector rib and said at leastone outer arc sector rib extend from said essentially planar rectangularbase different heights.
 4. The wafer container according to claim 1 thatfurther includes at least one additional rib that extends from saidbottom of said essentially rectangular base that is orthogonal to atleast one side of said bottom; a bi-directional locking feature hayingat least one set of locating ribs that extend from said essentiallyplanar base of said bottom housing that locate and capture opposingsides of said at least one additional rib that extends from said bottomof said essentially rectangular base that is orthogonal to at least oneside of said bottom, wherein said locking feature creates abi-directional lock of said top and said bottom housing to minimizerotation there between.
 5. The wafer container according to claim 4wherein said at least one additional rib that extends from said bottomof said essentially rectangular base that is orthogonal to at least oneside of said bottom is U-shaped and is orthogonal to three sides of saidbottom.
 6. The wafer container according to claim 5 wherein there arefour sets of said U-shaped rib.
 7. The wafer container according toclaim 5 wherein said bi-directional locking feature captures at leasttwo sides of said U-shaped rib.
 8. The wafer container according toclaim 1 wherein said at least one rib on said top housing has anorientation tab that extends normal to said rib on an outward directionof said circular orientation, and said at least one rib on said bottomhousing is configured to only clear said orientation tab when said tophousing and said bottom housing are placed in only one orientation. 9.The wafer container according to claim 8 wherein there are at least fourorientation tabs.
 10. The wafer container according to claim 8 whereinsaid orientation tabs prevent improper assembly of said top housing andsaid bottom housing members from being installed 90 degrees out ofalignment.
 11. The wafer container according to claim 8 wherein saidorientation tab is protectively located adjacent to a U-shaped rib thatextends from said essentially circular oriented rib.
 12. The wafercontainer according to claim 1 wherein said bottom housing has anundercut recessed pocket with a latch surface for a retention mechanismwherein said latch surface exists below said wafer supporting wall; saidlatch surface being formed in a molding process with the molding of saidbottom housing.
 13. The wafer container according to claim 12 whereinsaid latch surface is located at a height that is equal to or lower thanthe planar bottom surface of said bottom housing.
 14. The wafercontainer according to claim 12 wherein said latch surface further hasan angled or curved entry surface.
 15. The wafer container according toclaim 12 wherein said pocket further has at least two essentiallyvertical side walls to self-center said bottom housing on said retentionmechanism.
 16. The wafer container according to claim 1 wherein saidbottom housing has at least one latch that engages in a correspondingnotch located on said top housing, wherein said at least one latchsurface exists below said wafer supporting wall, and said a top surfaceof said latch is located at a height that is below a top surface of saidat least one rib.
 17. The wafer container according to claim 16 whereinsaid at least one latch includes at least four latches and fourcorresponding notches located in each corner region of said top housingor said bottom housing.
 18. The wafer container according to claim 16wherein said notch has a curve entry ramp and recess that elevates saidlatch above said entry ramp and lowers said latch into said recess toretain said latch in said recess when normal forces are applied to saidtop housing and said bottom housing.
 19. The wafer container accordingto claim 16 wherein said notch is located in a pocket that protects saidlatch during handling and impact.
 20. The wafer container according toclaim 1 wherein said bottom housing having an outer annular lip; saidtop housing having an outer annular lip that is configured to nest andfit within said outer annular lip of said bottom housing, and saidbottom housing further having a plurality of bearing ribs that extendfrom said essentially rectangular base to support said annular lip onsaid top housing.
 21. The wafer container according to claim 20 whereinsaid plurality of bearing ribs exist in at least four per quadrant onsaid bottom housing.
 22. The wafer container according to claim 20wherein said plurality of bearing ribs create a bearing surface of atleast 2.25 mm².
 23. The wafer container according to claim 20 whereinsaid plurality of bearing ribs reduce damage to at least one of stackingpads and the top rim of the housings.